The ultimate objective of this research program is to develop a set of ultrasonic techniques that takes full advantage of newly emerging ultrasonic contrast agents for quantitative clinical assessment of blood perfusion. Of particular importance are measurements in the eye. Ultrasonic contrast agents greatly enhance the visualization of vascular channels but they interact in a complex manner with incident ultrasonic energy. This project will expand theoretical analysis of contrast agent backscatter from various types of contrast agents. It will use these results in developing a set of complementary ultrasound methods for quantifying blood flow. Calibrated spectrum analysis of radio-frequency (rf) echo signals will be used to measure the effective concentrations of contrast agents. An novel dual-frequency-band technique will characterize low-frequency scattering and transmission phenomena by probing with high-resolution, high-frequency ultrasound. A transient depletion method will be used to estimate volume flow rates by studying the inflow of new particles into blood regions whose contrast agent particles have been depleted by brief increases in ultrasonic exposure levels. These techniques will be designed based on comprehensive theoretical analyses, and they will be validated in systematic laboratory measurements. They will then be applied in the in vivo rabbit eye, using segments of the ciliary body to model different types of vascularity. These animal studies will be conducted in collaboration with Cornell University Medical College, and will be coordinated with independent biological-effects studies of safety.